1. Field of the Invention
The present invention relates to a coil device functioning as a transformer or choke coil.
2. Description of the Related Art
FIG. 10A shows an exploded view of a conventional coil device. FIG. 10B shows a sectional view at the line Axe2x80x94A of the coil device shown in FIG. 10A. A coil device 1 shown in FIGS. 10A and 10B functions as a transformer or choke coil provided in a circuit such as a DCxe2x80x94DC converter and includes a substrate 2 for mounting an electronic component, a coil pattern section 3 provided on the substrate 2, a pair of core members 4a and 4b, and a core combining member 5.
On the substrate 2, electronic components defining a circuit are provided along with a circuit pattern. The substrate 2 is a multi-layered substrate defined by depositing a plurality of substrates on each other, and each substrate defining the substrate 2 has a coil pattern 7 provided coaxially about a central axis. The plurality of coil patterns 7 define a coil pattern section 3. In addition, when the coil device 1 defines a transformer device, among the plurality of coil patterns 7, at least one coil pattern 7 defines a primary coil while the others define secondary coils.
In this conventional example, both of the pair of core members 4a and 4b are made by pressing and sintering magnetic material powder such as ferrite, and are E-shaped core members having an E-shaped section and including a flat top-plate portion 8 and core legs 9a, 9b, and 9c extending from the center and bilateral ends of the top-plate portion 8.
On the substrate 2, core-leg insertion holes 10a, 10b, and 10c are provided at a position of the substrate located in the central portion of the coil pattern section 3 and at positions of the substrate located outside the coil pattern section 3, respectively. Into these core-leg insertion holes 10a, 10b, and 10c, the respective core legs 9a, 9b, and 9c of the core members 4a and 4b are inserted from the top and back surfaces of the substrate 2, such that the core legs 9 of the topside core member 4a and the core legs 9 of the backside core member 4b abutted each other.
The core-combining member 5 is a member for fitting and combining the pair of core members 4a and 4b together and is made by bending a metallic plate to have a top plate 12, legs 13, and claws 14. The top plate 12 is a plate covering a top surface 8a of the top-plate portion 8 of the core member 4a. The legs 13a and 13b are formed by bending lateral sides of the top plate 12 in an upward direction, and are arranged along the external side surfaces of the core legs 9a and 9c of the core members 4a and 4b. The claws 14a and 14b are formed by inwardly bending end sides of the legs 13a and 13b so as to abut the top surface 8a of the top plate 8 of the core member 4b. 
The distance h from the top surface 8a of the top-plate portion 8 of the core member 4a to the top surface 8a of the top-plate portion 8 of the core member 4b in the state that the core legs 9 of the topside core member 4a abut the core legs 9 of the backside core member 4b is substantially the same as the spacing between the top plate 12 and the claws 14. Thereby, the core-combining member 5 is fitted to the core members 4a and 4b in the state abutting each other so as to clamp both the lateral sides of the core members 4a and 4b in the state abutting each other with the top plate 12 and the claws 14 from both the top and backsides.
By utilizing such a core-combining member 5, the core members 4a and 4b are combined with each other in a movable state in the front and rear direction (xcex1 direction). In addition, the length W in the front and rear direction of each leg-insertion hole 10 is longer than the width w of core legs 9 of the core members 4 so as to allow movement of the core members 4 in the front and rear direction.
The coil device 1 is assembled as follows. For example, first, the core member 4a is placed on the top surface of the substrate 2 having the coil pattern section 3 and the leg-insertion holes 10 provided thereon while the core member 4b is placed on the back surface. Then, the legs 9 of the topside core member 4a are inserted into the respective leg-insertion holes 10 from the topside of the substrate 2. Similarly, the legs 9 of the backside core member 4b are inserted into the respective leg insertion holes 10 from the backside of the substrate 2. The core legs 9 of the topside core member 4a and the core legs 9 of the backside core member 4b are thus abutted to each other.
From the upper side of the core members 4a and 4b, the left leg 13a of the core-combining member 5 is inserted into the left leg-insertion hole 10a while the right leg 13b of the core-combining member 5 is inserted into the right leg-insertion hole 10c, at locations on either side of the core legs 9 of core members 4.
Thus, the top plate 12 of the core-combining member 5 is abutted to the top surface 8a of the top-plate portion 8 of the core member 4a while the claws 14a and 14b of the core-combining member 5 are abutted to the top surface 8a of the top-plate portion 8 of the core member 4b, such that the core members 4a and 4b that are abutted against each other are provided into the core-combining member 5. Thereby, the core members 4a and 4b are combined with the core-combining member 5 so as to be attached to the substrate 2. Simultaneously, the core members 4a and 4b clamp a portion of the coil pattern section 3 therebetween from the top and back sides of the substrate 2.
Thereafter, the combined core members 4a and 4b are slid with respect to each other in the front and rear direction such that abutting portions of the core members, i.e., abutted end-faces of the core legs 9, are rubbed together. By rubbing the end-faces of the core legs 9 together in such a manner (core rubbing), the following advantages are obtained.
That is, since the core members 4 are made by pressing and sintering magnetic material powder, the end-faces of the core legs 9 of the core members 4 have rough surfaces. During assembling the core members 4a and 4b, foreign particles often enter between the abutted end-faces of the core legs 9. Therefore, the degree of adhesion between the end-faces, which abut each other, of the core legs 9 is reduced, whereas when the end-faces of the core legs 9 are rubbed against each other, the end-faces of the core legs 9 are polished with each other so as to be close to mirror surfaces. Simultaneously, foreign particles which have entered between the end-faces of the core legs 9 are ground and removed, such that the end faces of the core legs 9 of the topside core member 4a are brought into tight contact with the end faces of the core legs 9 of the backside core member 4b. By bringing the core members 4a and 4b into tight contact with each other in such a manner, a reduction in inductance is effectively prevented, and thus, the performance of the coil device 1 is improved.
According to the conventional configuration, since bilateral sides of the pair of core members 4a and 4b are clamped by pressing them with the core-combining member 5 from both the top and back sides, when the cores are rubbed against each other, the core members 4a and 4b cannot be slid without a large amount force applied thereto, resulting in reduced efficiency in manufacturing.
Reduced thickness is also demanded for the coil device 1, and when the thickness of the core members 4a and 4b is reduced to meet the demand, the core members 4a and 4b are often broken by cracking or chipping, because of the large force that is applied to the core members 4a and 4b during the core rubbing. Thereby, preventing the thickness of the coil device 1 from being substantially reduced.
In order to overcome the problems described above, preferred embodiments of the present invention provide a coil device which greatly improves work efficiency during core rubbing in the manufacturing process of the coil device while preventing breaking of core members during the core rubbing when the thickness of the core member is reduced.
According to a preferred embodiment of the present invention, the core-combining member includes the topside cover member and backside cover member, and the pair of core members are clamped and combined by fitting the topside cover member and backside cover member to each other. Thereby, a greatly reduced clamping force must be applied from the core-combining member to the core members as compared with a conventional configuration.
Also, according to preferred embodiments of the present invention, the topside cover member and the backside cover member of the core-combining member are movable back and forth relative to one another in one direction along while the legs are fitted to each other. Therefore, by applying only a small force, the topside and backside core members are moved back and forth relative to one another in one direction while combining the core members together, thereby facilitating core rubbing so as to improve the efficiency of the core rubbing operation.
Since the pair of core members can be relatively moved back and forth in one direction so as to rub cores on each other by applying only a small force, even when the thickness of the core member is reduced, damage to the core member during the core rubbing is prevented. Therefore, the thickness of the core member can be reduced, resulting in a reduction in the thickness of the coil device.
Furthermore, the core-combining member is provided with a stopper, by which the relative movement of the topside cover member and the backside cover member is restricted, such that excessive relative movement of the topside cover member and the backside cover member is prevented.
The stopper has a simple structure including a leg opening and a projection, such that the structure of the core-combining member is not complicated.
According to the present invention, since the core-combining member itself is provided with the stopper, even when a substrate portion extending from a bilateral side-end of the coil pattern section to a substrate side-end is to be a cut-off section, the excessive relative movement of the topside cover member and the backside cover member is prevented. Therefore, by providing the cut-off sections, miniaturization of the substrate is achieved.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof with reference to the attached drawings.